A penetration test determines the relative values of density of the ground or soil in bore holes. A standard penetration test is made by determining the number of blows required by a standard weight dropped from a standard height to produce a standard penetration of 12 inches. A dynamic penetration test determines the relative density by recording the penetration per blow or for a specified number of blows. A static penetration test, on the contrary, pushes the testing device into the soil with a measurable force.
Normally this is accomplished simply by exerting the force downwardly on the top end of a drill string at whose bottom end is provided a standard point. In order to measure the static penetration resistance it is necessary to oppose this downward force with an enormous opposite force, normally by providing extremely secure anchors for the apparatus, or having the apparatus work from an extremely large--15-18 tons--piece of equipment. The amount of force necessary to move the entire drill string, in addition, somewhat falsifies the results given by such a test, as the lower end of the drill string might be in relatively soft ground but the overall resistance to displacement along the whole string might be high, giving a falsely high reading.